Cholinergic cells of the basal forebrain (cBF) and pedunculopontine nucleus (PPN) are implicated in Parkinson’s disease (PD), but current understanding of their role in PD symptomology is limited. Neuropathological and recent in vivo imaging research implies that cBF and PPN degeneration is associated with PD cognitive and mobility impairments. There remains a need to identify and validate widely accessible markers of cholinergic system degeneration to better understand its contribution to these symptoms. The aim of this thesis was to investigate how structural changes in the cBF and PPN relate to cortical activity and cognitive and mobility performance in people with PD, people with mild cognitive impairment (MCI), and healthy age-matched controls.
T1 and diffusion-weighted images were used in combination with stereotactic maps of the cBF and PPN to extract volumetric and diffusivity metrics from these regions as in vivo surrogate markers of structural integrity. These structural measures were assessed for their relationship with resting-state EEG, and cognitive and functional mobility performance.
People with PD showed reduced cBF volumes compared to healthy controls, and elevated PPN diffusivity compared to people with MCI. Subregional cBF volumes correlated with EEG changes in the theta-alpha range in people with PD and people with MCI. Volume loss in the cBF was also shown to mediate the relationship between executive function and Timed Up and Go dual-task performance in people with PD. PPN diffusivity metrics demonstrated correlations with cognitive performance and EEG changes in the alpha range in people with PD, and in the beta-gamma range in people with MCI.
Cortical activity measured with EEG may hold physiological relevance for structural changes occurring in the cBF and PPN. Volumetric loss in the cBF may impair the attentional-executive control of mobility functions. Elevated PPN diffusivity may impair attentional performance during tasks that require sensorimotor integration
